The present invention relates to resolver apparatus for receiving an electrical input signal representing a vector quantity and generating an electrical output signal corresponding to the vector quantity rotated through a given angle. In particular, the invention comprises fine and coarse-angle solid-state resolver apparatus having excellent resolution and low error.
Broadly defined, a resolver is a computing device which resolves an input vector into two orthogonal components in the plane of the input vector. Resolvers may also be used to effect the rotation of an input vector through a desired angle to produce an output vector angularly displaced from and coplanar with the input vector.
Typically, the resolver is an electro-mechanical device comprising input and output windings rotatable with respect to each other by positioning a shaft attached to one set of windings. Analog voltages corresponding to the orthogonal components of the input vector are applied to the input windings and the shaft is mechanically rotated through the desired angle to produce voltages at the output windings corresponding to the orthogonal components of the rotated input vector.
In my U.S. Pat. No. 3,974,367, granted Aug. 10, 1976, there is disclosed a low-cost, reliable solid-state resolver apparatus wherein the orthogonal components of the input vector are represented by analog voltages and the total angle through which the input vector is to be rotated can be represented by an analog voltage or digitally by an ordered set of logic levels.
This prior art solid-state resolver apparatus comprises a coarse-angle resolver and a fine-angle resolver connected in cascade. The coarse-angle resolver receives a vectorial input signal having first and second components corresponding to the orthogonal components of the input vector and the fine-angle resolver receives the vectorial signal at the output of the coarse-angle resolver. The coarse-angle resolver further comprises two sub-resolvers connected in cascade.
The input signal applied to the resolver apparatus disclosed in my aforementioned patent also includes a third component or angular input signal corresponding to the total angle through which the input vector is to be rotated. This third component of the input signal has two parts--a first part which corresponds to the coarse part of the total angle and a second part which corresponds to the fine part of the total angle. The first part of the third component of the input signal is, in turn, subdivided into a first portion for controlling one of the sub-resolvers and a second portion for controlling the other of the sub-resolvers. The voltage at the input of the second cascaded sub-resolver corresponds to the voltage applied to the first sub-resolver rotated through the first part of the total angle.
The second part of the third component of the input signal controls the fine-angle resolver to produce voltages at the output thereof which correspond closely to the orthogonal components produced by rotation of the signal applied to the input of the fine-angle resolver through the second part of the total angle. Thus, the voltages at the output of the resolver apparatus comprising the cascaded coarse-angle sub-resolvers and fine-angle resolver correspond closely to the orthogonal components produced by rotation of the signal applied to the input of the resolver apparatus through the total angle.
In my aforementioned patented resolver apparatus, the magnitude of the vector obtained by vectorially adding the orthogonal components at the output of the fine-angle resolver is the same as the magnitude of the input vector applied to the coarse-angle resolver. However, the angle of the output vector with respect to the input vector is not exactly equal to the total angle. Rather, it is slightly in error because the fine-angle resolver implements small-angle equations rather than the ideal resolver equations in order to reduce the complexity of the electronic hardware comprising the fine-angle resolver. This error can be as much as 0.014.degree. when the second part of the third component of the input signal is .+-.6.5.degree..